1. Field of the Invention
This invention relates to an auxiliary combustion chamber having no intake valve of an internal combustion engine which comprises a main combustion chamber having an intake and an exhaust valve, the auxiliary combustion chamber, a passage communicating the main and auxiliary combustion chambers, and an ignition spark plug whose electrode is positioned in the auxiliary combustion chamber.
2. Description of the Prior Art
It has been known to burn a lean fuel-air mixture so as to reduce such toxic substances as CO (carbon monoxide), HC (hydrocarbon) and NOX (nitrogen oxides) contained in the exhaust gas from internal combustion engines. However, such lean mixtures are not readily ignited and, in addition, are slow to propagate the flame, which results in the blow-by of the unburnt gas to the exhaust pipe or the reduction in thermal efficiency of the cycle. To overcome this, an internal combustion engine has been proposed that comprises a main combustion chamber having an intake and an exhaust valve and an auxiliary combustion chamber having an intake valve, wherein a lean fuel-air mixture is supplied to the main combustion chamber, while a relatively rich fuel-air mixture to the auxiliary combustion chamber, through their respective intake valves. In the internal combustion engine of this type, the relatively rich mixture in the auxiliary combustion chamber is first ignited and burnt, and then the lean mixture in the main combustion chamber is ignited by the flame from the auxiliary combustion chamber. This internal combustion engine equipped with the auxiliary combustion chamber having the intake valve has been very effective, insuring the combustion of the lean fuel-air mixture and propagating its flame rapidly. On the other hand, it is complex in structure because of the provision of the intake valve, which is opened and closed frequently, to the auxiliary combustion chamber and the provision of its kinds of mixture supply system for respective rich and lean mixture.
To eliminate the aforesaid shortcoming, the inventors have already proposed an internal combustion engine that comprises an auxiliary combustion chamber comprising a space having no intake valve, a main combustion chamber having an intake valve and an exhaust valve and communicated with said auxiliary combustion chamber through a passage, and an ignition plug whose electrode is situated in or near the passage of the auxiliary combustion chamber. In the internal combustion engine of this kind, a lean fuel-air mixture, which is drawn in through the intake valve on the intake stroke, is pushed into the auxiliary combustion chamber on the compression stroke, through the passage communicating the main and auxiliary combustion chambers. Because the elctrode of the ignition plug is placed in or near said passage, it is only the fuel-air mixture that exists thereabouts at the time of ignition. Accordingly, it ignites and burns the lean fuel-air mixture in the auxiliary combustion chamber, free from the influence of the burnt exhaust gas remaining therein. Subsequently, the lean fuel-air mixture in the main combustion chamber is burnt by the flame from the auxiliary combustion chamber.
However, in the above-described internal combustion engine, which has the auxiliary combustion chamber without the intake valve, the gas temperature in the auxiliary combustion chamber becomes very high, because combustion starts therein and the cooling effect of rich mixture is not available. This increases the quantity of toxic NOX contained in the exhaust gas produced in the auxiliary combustion chamber. Also, the auxiliary combustion chamber must be made of special metals, such as heat-resisting alloys, that are costly. Furthermore, there is a possibility that the auxiliary combustion chamber shell may move out of position by the frequent use of the engine under the influence of the high temperatures and pressures of said auxiliary combustion chamber.